One answer to your question below was in my earlier posts.  The short chain
polymers in the backcoat are more subject to hydrolysis than the long-chain
polymers in the recording surface.  In addition, once hydrolyzed, the
oligomer residue formed is more hydrophilic than the polymer matrix and
allow the tape to retain more moisture, inducing more hydrolysis.  One thing
that may not have been clear: it takes a longer exposure to high humidity
conditions, and higher humidity conditions over all, to hydrolyze the
long-chain polymers.  There are humidity conditions where short-chain
polymers will hydrolyze and long-chain polymers won't.  There are
short-chain  and medium-chain polymers in the recording surface but many
fewer than in the backcoat due to quality control when the polyester matrix
is created for the recording surface.  Some of the recording surface may
hydrolyze but not to the extent that it interferes with playback.

So, in answer to Richard's comments (didn't read till this post till after
my initial response here), there is a threshold at which hydrolysis will
occur and it is different for long, medium and short-chain polymers.  Also,
remember, hydrolysis is a bi-directional chemical reaction.  Not only is
there a threshold at which hydrolysis will occur, there is also a threshold
at which hydrolysis will run in the other direction and the oligomers will
cross-link back into polymers.  Testing has been done but the threshold is
dependent on the length of the polymers, the RH, the absolute humidity and
the temperature.  There are too many variables to give a "threshold" for
tape in general.

Another post by Tom- no, the Richardson-treated tape may well not go
"sticky" eventually, depending on the ongoing storage conditions (or it
might if the humidity is too high).  Some of the recording surface may
hydrolyze but, the greater concentration of long-chain polymers in the
recording surface that don't hydrolyze under "reasonably" low humidity
conditions , may not result in a "sticky" effect.  In International
standards (and laboratory testing), the hydrolysis issue is addressed, not
by if some of the binder hydrolyzes, but if sufficient hydrolysis residue is
present at any given time to interfere with playback.   As extreme examples:
if you store your tapes in 90% RH at 85 degrees, the tapes are very likely
to get "sticky" whether you have removed the backcoat or not.  Again, if you
store your tapes at 20% RH at 60 degrees, the tapes are unlikely to get
sticky whether you have removed the backcoat or not.  I don't know of
specific data about a set point of RH/temperature/ absolute humidity to
differentiate between when a backcoated and non-backcoated tape is likely to
produce enough oligomer residue to become "sticky".  There are factors
concerning the exact mix of long-chain/medium-chain/short-chain polymers in
the binder, whether any of the binder has already hydrolyzed before storage
at the "set point" and the tolerances of the playback machinery.  To make
matters more complicated, there are conditions where some of the polymers in
the binder are undergoing hydrolytic breakdown while, simultaneously,
oligomers in the binder are cross-linking back into polymers- messy for


-----Original Message-----
From: Association for Recorded Sound Discussion List
[mailto:[log in to unmask]] On Behalf Of Tom Fine
Sent: Thursday, January 21, 2016 7:55 PM
To: [log in to unmask]
Subject: Re: [ARSCLIST] One more sticky-shed data point - Richardson treated

Hi John:

I'm pretty sure Peter is aware of Richardson's work, but for those who
haven't dove deep into the weeds of tape degradation and playback ...

Charlie Richardson has developed a proprietary process, which he has not
described in detail or provided any public photos or videos of, which
removes the back-coat from sticky tapes. My assumption is that it involves
some sort of solvent and perhaps a scrubbing device that doesn't seem to
harm the oxide surface. He has claimed he does not first bake the tapes,
that he has a method where the tape will unspool and the back-coat is then
removed. Not having any evidence either way, I'll believe his claims until
proven otherwise.

A couple of years ago, I asked him to use his method to un-stick an old
Ampex test tape I had that I knew was sticky, based on attempted unspooling
of stuck tape at the beginning of the reel, and the fact that the look, feel
and smell of the tape was clearly Ampex 406 type. He sent me back the tape,
back-coat removed, and indeed it did playback with no problems. He asked to
keep the tape to perform "further tests and treatments," but I declined,
wishing to keep it under normal NY room-atmosphere conditions and seeing if
it went sticky again. So far, it has not. I will keep trying it out every
12 months or so and reporting back. When I started this thread some time
ago, my point was to say, this treatment did not render the tape unplayable
(as I feared it might), and it has kept the tape playable and
non-residue-creating for the past 2+ years. And this once again circles back
to one of my main questions -- if sticky shed is due to problems with the
binder, then why would removing the back-coat seem to first of all make a
tape un-sticky and second keep it un-sticky for a long period of time, if
not permanently?

-- Tom Fine